THE BICYCLE leaned against a pole. Unlocked and unattended. Forty-seven people walked past it.

One man didn't.

"Yo, whose bike is this?" he called to a trash-hauler pushing a Dumpster to a garbage truck idling nearby. The worker shrugged, and the man sprang into action.

So did Philadelphia police Officer Joe Ferrero.

Hidden but watching from a nearby shuttered storefront in the quiet Center City alley, Ferrero burst outside as the man hopped onto the fixed-gear bike and struggled to pedal away. He got barely a few feet, before Ferrero and his colleagues surrounded him, ordering him off the bike.

The man's eyes bulged in surprise. "Bike is supposed to be chained, supposed to be locked, that's why I thought there was nothing wrong with it," he protested, as one officer handcuffed him and another searched his backpack. "I never seen a bike unchained like that."

"You usually take things that aren't yours?" Ferrero responded.

Cops charged Phillip Ingram, 51, of North Philadelphia, with theft and receiving stolen property. A status hearing is scheduled for today .

Cops in Center City are trying an unusual approach to thwarting bike thieves: They're letting them steal bikes. Undercover cops like Ferrero set up stings - like the one Aug. 15 observed by the Daily News - leaving an unlocked "bait bike" out somewhere and then waiting for someone to take it.

They've logged more than a dozen arrests this way this year for a pesky quality-of-life crime that historically has had low arrest rates.

Bike enthusiasts support the stings - but say cops could be even more successful if they followed the lead of agencies elsewhere that hide GPS trackers on bait bikes - and then follow the thief back to his or her lair.

Such a strategy could help nab serial stealers who operate or supply bike chop shops or other organized theft rings, said Alex Doty, executive director of the Bicycle Coalition of Greater Philadelphia.

The issue is especially important in Philly, Doty said, because bike thieves increasingly prey on riders at a time when the city has dedicated bicycle lanes on many city streets and otherwise encourages the public to pedal.

"We have almost twice as many bicycle commuters as any other large city in the United States," Doty said. "There are crimes that certainly rank a lot higher than bike theft, but for bicyclists this is a big problem. It certainly deters people from bicycling."

Philadelphia in 2008 ranked first in a Top 10 list compiled by lock-maker Kryptonite of the worst U.S. cities for bike theft. (The company no longer compiles a list.) And Azavea, an analytical firm that was asked by Doty's coalition to examine bike thefts, found that about 11,000 bicycles were reported stolen from 2007 through 2012 in Philly.

Doty and other bike enthusiasts say actual bike thefts are far more common, though, because many victims don't report them.

'I didn't report it'

Aliza Olive didn't tell police when someone stole her locked Giant mountain bike in July from her back patio in the Graduate Hospital neighborhood.

"It was a bike that I had bought used about three weeks earlier from my boyfriend's cousin for about $40," said Olive, 30. "I didn't report it, because I didn't think it was worth it; the chances of it being found are so slim, and it was only $40. I just got another bike off Craigslist for $30."

But as bike thefts rise, Ferrero and colleagues in Center City's Sixth District say they're redoubling efforts to nab offenders.

They set up stings whenever crimes spike. Besides bikes, they also leave laptops unattended on cafe tables and purses on passenger seats in unlocked cars, swarming the minute a thief pounces.

Civil libertarians decry such stings as entrapment, but the way Capt. Brian Korn sees it, anyone who bites on the bait doesn't deserve sympathy.

"We're merely presenting an opportunity," said Korn, the Sixth District's commander. "Honest people walk by all the time. We even have people call in [to police] and say, 'Hey, there's a bike here unattended.' "

Old-fashioned sleuthing still works. When someone stole 15 bicycles from the Irish Pub in Center City after its annual Tour de Shore charity ride in July, police were able to arrest suspected thief Daniel Byrd after spotting him on surveillance video, allegedly whisking the bikes away in a pickup truck. Byrd, 21, of Spring Garden, is scheduled for a preliminary hearing Thursday.

Bike enthusiasts have started a Facebook page called Philadelphia Stolen Bikes to report thefts, share advice and commiserate about bike bothers, big and small.

Bryan Hance thinks the bicycling community is its own best bet for nabbing bike thieves, given that police departments often prioritize more serious crimes.

Hance, of Portland, Ore., was just a "computer-science guy" when some punk stole his bike in the mid-1990s. Then another thug stole his replacement bike - and the one after that. In all, Hance figures he's been victimized by bike thieves eight times, including a bike taken from his Tucson, Ariz., living room while he was taking a shower.

So Hance decided to put his computer skills to work to beat the bad guys.

He created stolenbicycle registry.com, a free online database for bicyclists - and bike shops, cops, pawn shops or anyone who might encounter stolen bikes - to register and search for their stolen bikes. He also started Twitter feeds for cities, including Philadelphia, that have high bike-theft rates.